Currently, pressure of an earth formation is measured from within a borehole by using a tool such as the RFT (Mark of Schlumberger; Repeat Formation Tester) or the MDT (Mark of Schlumberger; Modular Dynamic Tester), for example. A tool of the MDT type is generally described in U.S. Pat. No. 4,860,581 to Zimmerman et al. Briefly, the tool is lowered into a borehole and a packer of the tool is placed against a portion of the borehole wall to isolate that portion of the formation from borehole fluids. The packer surrounds a probe. As a "draw-down" pressure is applied at the probe, pressure at the isolated portion of the borehole wall decreases to a pressure substantially below that of the formation. This draw-down pressure effectively cleans the isolated portion of the borehole wall by drawing mudcake from the borehole wall via the probe. This facilitates fluid flow from the formation. The probe then is filled with formation fluid, during the applied draw-down. The pressure inside the probe is lower than the formation pressure as a result. A pressure gauge connected to the chamber then indicates pressure of the earth formation.